1. Field of the Invention
The present invention relates to a noise reduced contactless parallel data transfer device and method thereof for transferring a signal and voltage on a contactless and parallel basis and more particularly to a contactless parallel data transfer device and method thereof which are used for a portable memory such as a memory card.
2. Description of the Prior Art
A contactless transfer card using an electromagnetic coil has been used as a contactless connection means for supplying data to a memory card recently. For example, as indicated in Japanese Patent Application Laid-Open 3-232207, it is a method that pairs of transmitting coils and receiving coils which have a one-to-one correspondence with each other are installed and necessary data as a 1-bit data signal string is transmitted or received by electromagnetic coupling.
As a type that crosstalk between the neighboring transfer coils is prevented, a device wherein a plurality of transmitting and receiving coils are installed separately from a coil for power supply for data transfer so as to transfer a plurality of bits at the same time and a shield structure is provided between the coils so as to prevent mutual interference between the bits (crosstalk between the bits) is indicated in Japanese Patent Application Laid-Open 4-23990.
On the other hand, as a method for reducing noise which is induced in the power cable and grounding cable, as indicated in Japanese Patent Application Laid-Open 4-254993, there is a type that the driving timing between bits is shifted. Furthermore, as indicated in Japanese Patent Application Laid-Open 5-114055, there is a method that a means for canceling the low frequency component which is induced on the power cable between a pair of transfer coils on the card side is provided.
In Japanese Patent Application Laid-Open 3-232207 and Japanese Patent Application Laid-Open 4-23990 of the aforementioned prior arts, firstly there is a problem imposed that an extremely large peak current which is generated necessarily when large-amplitude information pulses are sent at high speed in parallel by electromagnetic coupling is not taken into account, and not only the scale of power circuit supplied from the outside by electromagnetic coupling becomes large but also a highenergy pulse variation is generated in total, causing crosstalk between the neighboring transfer coils, and the probability of a malfunction in the card becomes high, causing reduction of the reliability.
Particularly as a plurality of transfer coils are mounted in higher density, crosstalk between the coils which is generated necessarily is increased and causes disturbance of highly densed installation of transfer coils.
It is known that an electromagnetic shield means is provided between the coils as a countermeasure therefor. However, it is impossible to shield all the coils, and an effect by the leakage field from the peripheral coils cannot be ignored, and they are obstacles for the practical realization of contactless parallel transfer oils.
Secondly, there is a problem imposed in the energy concentration when parallel transfer pulse signals are example, if 16 channels transfer "1" at the same time when it is assumed that a driving current of 10 mA is necessary for each coupling coil (each channel), a pulse current of 160 mA including an extremely high frequency component is generated. Therefore, a high capacity of the driving source is required and furthermore noise is induced in the power lines. Not only such an instantaneous current is generated but also the power consumption of the peripheral circuit is increased in proportion to speeding-up of the data transfer rate and they are obstacles for the realization of high speed transfer.
Furthermore thirdly, there is problem imposed that in spite of the contactless type using no connector, front-rear reverse insertion is not taken into account, and restrictions for users are imposed, and the operability is not improved.